Massive 100-year floods, like the one Laguna Beach experienced two years ago that raged through Laguna Canyon neighborhoods and sent overflowing runoff and sediment through downtown shops, will happen every year in less than 40 years, according to an expert in flood-water mapping.

While floods of that magnitude have a slight 1 percent probability of occurring in any year, the quickening rate is due to a number of increasingly compounding factors, Brett Sanders, chair of UC Irvine’s civil and environmental engineering department, told Laguna Greenbelt members at their annual meeting last Thursday. Factors include global warming, urban run-off from overwatering, over-using water for showering and frequent flushing, high surf and surges, and astronomical high tides, he said.

“Southern California actually jumped out as an area where floods are going to become much more frequent,” Sanders predicted. “By 2050, 100-year floods facing the coastal areas of Southern California are going to be an annual occurrence.”

The ocean is definitely rising more than usual from the effects of global warming, said Sanders. Research, including satellite mapping, puts the rise of the ocean at three millimeters a year.

“We have flooding problems now,” Sanders said to an audience of mostly long-time property owners. “That’s an alarming figure.”

Reducing greenhouse gases by driving less or using nonpetroleum-dependent transportation would help mitigate global warming, he said, “but I don’t think we’re doing too well with that.”

Exacerbating these convergences, atmospheric pressures periodically produce El Nino conditions that warm and expand ocean waters and can often result in huge downpours.

In other words, a nexus of portentous elements could make for the perfect flood in Laguna Beach, where downtown is just feet above sea level.

Such predictions haven’t gone unnoticed. The City Council recently adopted a flood-damage prevention ordinance that requires businesses within the 100-year floodplains, which includes Laguna Canyon Creek, Aliso Creek and near-sea-level businesses, to install floodgates. The 2010 flood damaged 59 businesses at a loss of $3.5 million, most of which could have been prevented with floodgates, according to city staff. And the city has approved installing an early flood warning systems that will relay information to residents and businesses via reverse 911 calls.

The ordinance also specifically addresses rising sea levels, requiring developers to factor in projected increases in determining flood protection. Levels in Laguna are rising, according to a city report, and will continue to climb from five to nearly 30 inches by 2050 and up to 65.5 inches by 2100.

Council member Toni Iseman, who attended the Greenbelt meeting, pointed out that rising sea level projections where addressed in designing the city’s new $8.1-million lifeguard headquarters. “The city’s on it,” she said.

California is more susceptible to flooding, said Sanders, compared to the East and Gulf coasts, where 100-year-floods will step up to one every 50 years. “We don’t have any history of defending against major surges in Southern California, no infrastructure with communities right up to the high-tide mark,” he explained. Other parts of the country that experience hurricanes have built tidal walls to protect against high tides as well as storm surges.

California has other unique natural anomalies, including wind phenomena and earthquake fault lines.

Ocean levels in Southern California have flattened out since the 1980s due to “decadal oscillation,” geek-speak for a wind that hangs around for decades, which can create a false sense of calm. Scientists are predicting that the fair winds will soon change.

“There’s a wind stress on the ocean right now that’s basically pushing water away from the West Coast,” Sanders said, “and towards the eastern side.” The Seattle, San Francisco and San Diego regions are experiencing the same phenomenon. “Sea levels will resume, jump up and catch up,” he cautioned. “We could see in the matter of just one year several centimeters of sea level rise as opposed to seeing millimeters a year.”

As for fault lines, no one is saying that the San Andreas crack will make its final break and drop half of California into the briny brink, he said, but scientists are documenting that land mass on the coast side is settling. “If the land is sinking,” delineated Sanders, whose research is funded and corroborated by the National Science Foundation in Arlington, Va., “that could cause local sea levels to rise.”

His solution? Learn to live with it. How? By changing behavior.

“I don’t think insurance companies are going to be there forever for flood risks,” he said. Individual accountability will become key. “What are the risks of your property?” he suggested as starter questions. “Would that change your behavior? Would you retrofit your house? Would you raise your foundation? I’d be curious to see if that would be more effective in trying to manage a risk than, say, being given a flood map that just says you’re in a flood plain.”

The first defense is to predict flooding and plan accordingly. “With a two-hour forecast of a flood, people can reduce their losses by 50 percent.”

In Italy, mud-jacking is used to elevate entire cities, he said. Wells are dug under sinking sites and slowly injected with mud until buildings and streets begin to rise. The ports of Los Angeles and Long Beach also have been raising land for years, he said, due to oil and gas exploration, which causes the land surface to cave in.

Under an NSF grant, Sanders is collaborating with the city of Newport Beach, where protecting high-priced property is high priority, on ways to prevent flooding. Balboa Island, Little Balboa Island, Linda Isle and Lido Isle in Newport Harbor already sit below sea level. The islands started out as sandbars that were built up and built on. “At some level, it’s all constructed shoreline,” he said.

But his research in Newport is finding that a seawall to protect against tide-driven flooding, which keeps the bayside communities dry most of the time, makes wave-driven flooding worse. “Water comes up over the beach, hits the wall, ponds behind the wall, spreads out and isn’t able to drain back into the bay,” he said.

“When ocean conditions change we can change with it,” he said. “Retreat, accommodate or defend. That’s the questions you have to answer.”